We do not here propose to sketch the development of the idea, either before or after Darwin; but only, in the first place, to state the grounds on which the belief in Evolution is based, and, in the second, to trace roughly the lines along which animal Evolution has proceeded. In the first few pages of this book, then, we shall endeavour to bring forward some of the evidence on which the modern Evolution theory rests. +--------------+------------------+---------------+------------------+ | | First Appearance |Dominant Types.| | | | of Types. | | | +--------------+------------------+---------------+------------------+ | Modern | ... | MAN | } Post-tertiary, | | Diluvium | Man | ... | } 1/2 per cent. | +--------------+------------------+---------------+------------------+ | Pliocene | ... | } | } Tertiary or | | Miocene | Monkeys | } MAMMALS | } Cænozoic, | | Oligocene | ... | } | } 2-1/2 per cent.| | Eocene | Lemurs | } | } | +--------------+------------------+---------------+------------------+ | Cretaceous | _Higher mammals_ | } | } Secondary or | | Jurassic | { _Birds_ | } REPTILES | } Mesozoic, | | | { Marsupials | } | } 11 per cent. | | Triassic | _Monotremes_ | } | } | +--------------+------------------+---------------+------------------+ | Permian | _Reptiles_ | AMPHIBIANS | } Primary or | | Carboniferous| _Amphibians_ | } FISHES | } Palæozoic, | | Devonian | _Lung fishes_ | } | } 32 per cent. | | Silurian | _Lower fishes_ | ... | } | +--------------+------------------+---------------+------------------+ | Cambrian | ... | ... | } Archäen, 54 | | Laurentian | ... | ... | } per cent. | +--------------+------------------+---------------+------------------+ FIG. 2.--Table showing the chronological succession of the stratified rocks, the subdivision of geological time, the approximate position of the earliest fossils of each of the main types of vertebrates, and the period of domination of each group. As our first witness, we may call the rocks which constitute the outer portion of the earth, and ask them to tell us what they remember of the history of life upon the planet. We cannot hope for the whole truth from them, for their memory is imperfect; and yet they can tell us a great number of important facts. [Illustration: THE EVOLUTION OF THE HORSE FIG. 3. From _The Guide to the American Museum of Natural History_.]